Patent GB-1235747-A (GB)
Title: Antifoggants for photographic products and processes
IPC: G03C8/06
Filed: 1968-12-11
Abstract: 1,235,747. Pyrido imidazoles. INTERNATIONAL POLAROID CORP. 11 Dec., 1968 [11 Dec., 1967], No. 58958/68. Heading C2C. [Also in Divisions C3 and G2] 5 - Amino - 4-azabenzimidazole dihydrochloride is prepared by adding 2,3,6-triamino-pyridinedihydrochloride to 98-100% formic acid, refluxing and evaporating to dryness and then treating the residue with concentrated hydrochloric acid. 2,3,6 - Triamino - pyridine dihydrochloride is prepared by reducing a mixture of 2,6-diamino- 3-phenylazo pyridine hydrochloride, water and concentrated hydrochloric acid with 5% platinum on charcoal at 40 p.s.i - at room temperature. 6 - Nitro - 5 - amino - 4 - azabenzimidazole is prepared by nitrating 5-amino-4-azabenzimidazole - dihydrochloride (prepared as above) with sulphuric acid (specific gravity 1.42) and a 50% solution of nitric acid (specific gravity 1.84). 5,6 - Imidazo - 4 - azabenzimidazole is prepared by reducing 6-nitro-5-amino-4-azabenzimidazole (prepared as above) in water and ethanol with platinum on carbon catalyst and platinum oxide in a hydrogenator under 40 p.s.i. and the product is then treated with an excess of 97% formic acid. 5 - Hydroxy - 4 - azabenzimidazole is prepared by adding 5-amino-4-azabenzimidazole dihydrochloride (prepared as above) to a sulphuric acid solution, cooling and adding dropwise a solution of sodium nitrite in water, and then neutralizing the solution with 10% sodium hydroxide. 5 - Methane - sulphonamido - 4 - azabenzimidazole hemihydrate is prepared by adding a 50% sodium hydroxide solution dropwise to a stirred solution of 5-amino-4-azabenzimidazole dihydrochloride (prepared as above) and adding dropwise to the resulting suspension methanesulphonyl chloride followed by further 50% solution of sodium hydroxide. 5 - Bromo - 4 - azabenzimidazole is prepared by adding bromine to a solution of 5-amino-4- azabenzimidazole dihydrochloride (prepared as above) in a 48% solution of hydrobromic acid cooled to -10 C., then adding a solution of sodium nitrite in water at 0 C. and cooling to -10 C. and adding a solution of sodium hydroxide. 6 - Chloro - 4 - azabenzimidazole is prepared by refluxing a solution of 5-chloro-2,3-diaminopyridine in 98-100% formic acid, evaporating to dryness in a rotary evaporator, dissolving in boiling water, treating with charcoal and filtering the mixture when hot and extracting the charcoal residue. 6 - Bromo - 4 - azabenzimidazole is prepared similarly using 5-bromo-2,3-diamino-pyridine as the starting material. 2 - Methyl - 6 - chloro - 4 - azabenzimidazole is prepared similarly by refluxing 5-chloro-2,3- diamino-pyridine with acetic anhydride. 6 - Bromo - 5 - methyl - 4 - azabenzimidazole is prepared by refluxing 2,3-diamino-5-bromo-6- methyl-pyridine with 98-100% formic acid. 2,3 - Diamino - 5 - bromo - 6 - methyl - pyridine is prepared by the hydrogenation in the presence of Raney (Registered Trade Mark) nickel of 2 - amino - 3 - nitro - 5 - bromo - 6 - methylpyridine. 2 - Amino - 3 - nitro - 5 - bromo - 6 - methylpyridine is prepared by adding slowly 2-amino-5- bromo-6-methyl-pyridine to concentrated sulphuric acid cooled to 20 C., warming to 55 C. and adding dropwise concentrated nitric acid so that the temperature remains below 60 C. 2 - Amino - 5 - bromo - 6 - methyl - pyridine is prepared by adding bromine dropwise to a solution of 2-amino-6-methyl-pyridine in 20% sulphuric acid cooled in ice water, and the resultant colourless solution was made alkaline by adding ice cold aqueous 20% sodium hydroxide dropwise. 5-Methyl-4-azabenzimidazole is prepared by hydrogenating 5 - methyl - 6 - bromo - 4 - azabenzimidazole (prepared as above) in the presence of 5% platinum on charcoal catalyst and platinum oxide together with 1% sodium hydroxide solution.